Conventionally, an electric connection box having various electric components such as a relay, a fuse and the like mounted thereon is provided in an automobile. An electric component connection unit accommodated in the electric connection box includes an electric component mounting block having electric components mounted thereon and an insertion permission frame which permits the electric component mounting block to be inserted thereinto and is accommodated in a lower cover of the electric connection box.
As the electric connection box is vibrated by the running of a vehicle, the electric component mounting block inserted into the insertion permission frame is vibrated with respect to the insertion permission frame. As a result, the electric component mounting block is, for example, abraded by the insertion permission frame and thus is disengaged therefrom unexpectedly. Thus, there is an undesirable possibility that a secure electric connection state cannot be provided.
In such a situation, various measures have been taken in order to allow the electric component mounting block to be integrated with the insertion permission frame without becoming unstable with respect thereto even when the electric component mounting block is vibrated.
Patent Document 1 discloses a “cassette relay assembly structure”, which is one example of structure for assembling a relay block as the electric component mounting block and a cassette frame as the insertion permission frame. One of the above-described measure is taken for the “cassette relay assembly structure”.
The “cassette relay assembly structure” described in Patent Document 1 has the following structure. On an inner wall of the cassette frame, ribs (23, 24) protruding toward the cassette relay block along an insertion direction in which the cassette relay block is inserted into the cassette frame are formed. On an outer wall of the cassette relay block, ribs (11, 12) protruding toward the cassette frame along the insertion direction are formed.
According to the “cassette relay assembly structure” described in Patent Document 1, in a state where the cassette relay block is inserted into the cassette frame, one face of each of the ribs (23, 24) protruding from the cassette frame and one face of each of the ribs (11, 12) protruding from the cassette relay block are put into contact with each other. Owing to this, the cassette relay block can be inserted into the cassette frame without being positionally shifted or inclined.
This will be described in more detail. The rib (11) protruding from each surface of the cassette relay block facing the cassette frame, and the rib (23) protruding from each surface of the cassette frame facing the cassette relay block, are in contact with each other. The rib (12) protruding from each surface of the cassette relay block facing the cassette frame, and the rib (24) from each surface of the cassette frame facing the cassette relay block, are in contact with each other at a position which is away by a prescribed distance from the position where the rib (11) and the rib (23) are in contact with each other.
Owing to this, the cassette relay block is positioned with respect to the cassette frame at a total of two positions between each surface of the cassette relay block and a surface of the cassette frame facing the each surface.
Often times, the ribs formed on the cassette relay block and the cassette frame are not formed at exactly the desired positions but are inevitably formed at positions shifted from the desired positions due to a processing error or the like. Such a positional error regarding the formation of the ribs exerts an adverse influence on the positioning precision of the cassette relay block with respect to the cassette frame.
In the “cassette relay assembly structure” described in Patent Document 1, two or more ribs protruding in a direction perpendicular to a prescribed direction are located at positions which are away from each other by a prescribed distance as described above. Especially such a structure where two ribs are at separate positions causes a disadvantage that the errors of the ribs at the separate positions are accumulated in the prescribed direction. Thus, the adverse influence of the errors regarding the formation of the ribs is exerted more significantly.
As a result, the cassette relay block cannot be firmly positioned with respect to the cassette frame, and thus easily becomes unstable. This causes a problem that the cassette relay block is easily abraded and thus an electrically superb connection state cannot be kept easily.
The influence of the errors regarding the formation of the two ribs at separate positions may cause a problem that the cassette relay block is, for example, stuck when being inserted into the cassette frame and thus cannot be smoothly inserted.